Infrared thermometers (clinical thermometers) generally includes probes projected from the casing of the main body of the thermometer so as to be insertable into the external auditory canals of human beings. Waveguides are provided inside the probe to guide the infrared rays radiated from biological surface tissues, such as external auditory canals and tympanic membranes, to infrared sensors.
FIG. 5 shows schematically one example of the internal structures of the probes of infrared thermometers. In this infrared thermometer, the probe 100 is composed of a conical tube hollow inside, and the infrared sensor 104 is provided in the end portion of the probe 110, the end portion having a large diameter and being fixed to the main casing body 102 of the thermometer. One end of the tubular waveguide 106 is fixed to the detecting face of the infrared sensor 104, and the other end of the waveguide 106 is positioned in the vicinity of the tip end of the probe 100 with a small diameter. The temperature sensor 108 measuring the temperature of the infrared sensor 104 is provided on the infrared sensor 104. The infrared sensor 104 and the temperature sensor 108 are included in the casing main body 102, and are connected to the arithmetic operating section 110 operating arithmetically the temperature of an object based on the outputs from the sensors 104 and 108. When measuring a bodily temperature using this thermometer, the probe 100 is put into an external auditory canal 112. The infrared rays radiated from the external auditory canal 112 and the tympanic membrane 114 reach the infrared sensor 104 through the waveguide 106, so that the bodily temperature is computed by the temperature operating section 110 based on the outputs from the infrared sensor 104 and the temperature sensor 108.
When there is a difference in temperature between the waveguide 106 and the infrared sensor 104, the above infrared thermometer causes an error in the measuring result of the infrared sensor 104 due to the difference in temperature. The waveguide 106 is made of a high thermal conductive metal in order to prevent such an error, and its interior wall is usually mirror finished and further plated with gold. In addition, the waveguide 106 is welded at its end to the infrared sensor 104 by heating, without any thermally insulating material between them.
When the probe 100 is inserted into the external auditory canal 112, a part of the outer circumferential surface of the probe 100 is unavoidably put into contact with the external auditory canal 112. At this point of time, the heat of the external auditory canal 112 is transmitted to the probe 100 because the temperature of the probe 100 is usually lower than that of the external auditory canal 112. The heat of the probe 100 is further transmitted to the waveguide 106, raising the temperature of a part of the waveguide 106. As a result, the infrared sensor 104 detects the raised temperature of the part of the waveguide 106, causing an error in the measurement of the bodily temperature.
In order to solve the above problem, Japanese Unexamined Patent Publication No. 61-117422 discloses a method of measuring a temperature in which the probe is preheated to a predetermined reference temperature before measurement of a bodily temperature to thereby prevent the temperature of a part of the waveguide from rising above the temperature of the infrared sensor during the measurement. This method, however, has a problem that the external auditory canal and tympanic membrane become warm by the preheated probe, so that a precise bodily temperature can not be measured. Further, preheating the probe consumes more electric power, so that the service lives of batteries are remarkably decreased, particularly in case of a portable thermometer using batteries.
Japanese Unexamined Patent Publication No. 6-502099 (Japanese Patent Application No. 4-504325) discloses an infrared thermometer comprising an infrared sensor, ambient temperature sensor and waveguide temperature sensor. This infrared thermometer utilizes an object's temperature-conversing method (i.e. calibration mapping) in which the temperatures of the environment and an object are multi-measured when the apparatus is adjusted, and in which the temperature of the object is converted using the outputs from the respective sensors and a temperature-converting equation which has been determined experimentally. This infrared thermometer, however, requires a plural number of temperature sensors with consequently a high production cost, and it requires measurement of a plurality of ambient temperatures for adjusting the apparatus, so that it takes a long time in adjusting the apparatus.